Various types of electrically-actuated mechanisms have been developed for extending and retracting locking devices such as deadbolts. Such devices allow a deadbolt on a door or a similar moving device to be retracted by an operator such as a security guard at a remote and protected location.
For example, U.S. Pat. No. 1,768,021 (Bauerband 1930) discloses a deadbolt which is mounted on the end of a door and which protrudes outwardly. Rather than a swinging door mounted on hinges, the door is a sliding door mounted on rollers, so that when it is pushed against the closure frame, the bolt will be inserted by the door movement into the opening of the latching device. In the process, the tip of the bolt pushes back a spring-mounted detente, which normally holds back a movable pin in a solenoid. When the detente is pushed out of the way by the bolt, the pin is released; it drops and passes through a slot in the bolt, thereby locking the door in its closed position. The door is unlocked by energizing the solenoid, which raises the pin. The door must be opened while the solenoid remains energized. After the door is opened, the spring-loaded detente keeps the pin lifted out of the path of the bolt, so the door can be closed later without operating the solenoid.
U.S. Pat. No. 2,798,751 (Walden 1957) also discloses a lock device operated by a solenoid. The solenoid, when energized, lifts a vertically mounted solenoid pin. The pin is connected to one rotating lever, which in turn is coupled to a second rotating lever, which in turn is coupled to a swinging lever which can swing in either of two directions, depending on whether the deadbolt was open or closed when the solenoid was energized. The swinging lever is coupled to the deadbolt via an indirect linkage involving two more moving pieces, so that when the lever swings in either direction, the deadbolt either retracts (to unlock the door) or extends (to lock it again). The deadbolt is retracted by operating the solenoid, and it remains retracted so the door can be opened or closed any number of times, until the solenoid is operated again.
Despite their advantages, the locking devices of the prior art suffer from various limitations. For example, the locking device of Bauerband must be located on a sliding door rather than a hinged door, and the outward protrusion of the exposed deadbolt can lead to problems such as bending and tampering. The device of Walden requires at least nine different moving parts, not including the various hinge screws, and if a single one of those parts or hinges becomes jammed, frozen, corroded, or gummed, the entire locking device can be rendered totally inoperative. In addition, that multiplicity of parts makes the device expensive to manufacture and assemble, and difficult to repair. Furthermore, since the swinging lever of the Walden device requires unconstrained motion without generating a large amount of momentum, the use of grease to lubricate and protect the internal parts can generate problems.
One of the most crucial need for locks used by prisons is durability. A single locked door in a prison is often locked and unlocked several hundred times each day. Under those conditions, they can become so worn within six months that they can no longer be repaired by a professional locksmith and must be replaced.
One object of the present invention, therefore, is to provide a durable, heavy-duty lock which can offer extended, reliable performance despite heavy use.
Another object of this invention is to provide a locking mechanism with a minimal number of moving parts, any of which can be replaced easily to prolong the useful life of the assembly.
Another object of the present invention is to provide a relatively simple and inexpensive but reliable locking mechanism which can be opened by a remote operator.
Another object of this invention is to provide a solenoid-operated door bolt which, once retracted remains retracted until the door is closed.
Another object is to teach the construction and operation of a locking device which goes automatically into a locked condition when the door on which it is installed closes, without requiring further operation of the solenoid.
Another object of this invention is to provide a locking system especially adapted for use in locations which require a high level of security, such as prisons and military bases.
Another object is to provide a locking device which is difficult for unauthorized persons to unlock or tamper with.
Another object is to provide a locking device that is relatively compact and is relatively easy to install without requiring extensive adjustment.
Another object is to provide a locking device which is aided by gravity and by mechanical force to move to a latched condition when the door on which it is installed is closed.